Inflow Control Device Optimization Design For Horizontal Well In Bottom Water Reservoir

Horizontal wells have been widely used in oil and gas development, however, the heel-toe effect and reservoir heterogeneity initiate unbalanced inflow along well bore, which lead to low oil production and recovery, especially for those extended reach ones. Gas and/or water cresting invade unevenly and break into well bore from heel end or high permeability zone if gas cap and/or bottom water exist, and further depress oil production and recovery, or even shutdown the well. The problem mentioned above has not been solved effectively in well completion study field in China. To this point, the technology of inflow control device(ICD), which has been widely applied abroad, was discussed in detail, including operating principle, classification, tool structure and field application. The author focused on nozzle type ICD and established a set of theory methods for arranging ICD screen pipes in order to promote ICD technology in China and attain independent intellectual property rights.This thesis consists of two parts:model introduction and parameter analysis. In the former part, horizontal well in bottom water reservoir was selected as study object, and an oil and water two-phase coupling model was established and solved by numerical reservoir simulation method. The coupling model contained three kinds of flow process:reservoir seepage, well bore conduit flow and throttle nozzle jet, and was formatted in hybrid grid which could reflect key characteristics of seepage in reservoir both near and far away from well bore. Subsequently, horizontal well production performances under conventional completion and ICD completion were calculated by "simple iteration SEQ method"; The later part concentrated on the impact of throttling segment length, quantity ratio of blank vs. screen pipe in throttling segment, nominal diameter nozzle in ICD pipe and ECP settling position on production, ICD screen arrangement principles were then established.The innovations in this study state as follow:(1)A new kind of ICD completion string combing ICD screen pipe and blank pipe was used, arranging blank pipes in throttling section could help to collect more reservoir produced fluid into ICD pipes, and then give full play to throttling ability of nozzles, further more, arranging blank pipes cut the cost of completion operation;(2)In order to simplify calculation, pseudo transmissivity, which could quantify the well bore conduit flow and throttle nozzle jet, were created respectively, refering to reservoir seepage transmissivity. Pseudo transmissivity unified mathematical expression of these three kinds of flow, and ensured that reservoir seepage finite difference equations could apply to the entire hybrid grid system;(3)A "simple iteration SEQ method" was created and used in solution, outside loop with terminal condition of mass conservation was established after entire horizontal well production segment was treated as control body. Iteration convergence and stability were intensified when the three main calculation procedures of SEQ method run as loop body of the simple iteration;(4)Design target of ICD screen arrangement plan was proposed when profile control indicators (i.e. the target profile) under homogeneous reservoir and heterogeneous reservoir condition were available. Special Gini coefficient was then put forward to evaluate deviation between flow rate profile under current completion method and profile control indicator;(5)Six principles of ICD screen arrangement were investigated and sequenced according to importance in order to guide optimizations;Calculation come to results and conclusions that:(1)ICD technology observably improved the inflow profile of horizontal wells. ICDs balance the water cresting, extend breakthrough time of bottom water, raise oil production during water-free production period, and enable horizontal well to produce under high pressure drawdown;(2)Pressure drawdown is usually small in toe end, ICD screen pipes are not necessary in its neighboring well bore sector and can be replaced by stand alone screen in order to cut the cost, but its adjustment capacity is lower than that of throttling along the entire well bore. Results show that bottom water invasion to toe end is reinforced because of the fluid’s natural feature of flowing along the minimum flow resistance path when throttle strength is high in heel end. Pressure and saturation influence each other, and saturation is more sensitive;(3)ICD completion string with less blank pipes has stronger profile control capability. However, reducing blank pipes quantity in throttling section decrease the collected flux in each ICD screen, and make nozzles too small in size, thereby, ICD string will lose advantages in manufacturing, reliability and cost;(4)ICD completion string distributed with different nominal diameter nozzles complicate field assembly, the one arranged with uniform nominal diameter nozzles become popular due to strong practicability and also have enough throttle ability. Results indicate that smaller nozzles in size lead to more balanced profile, but will be stuck with excessive manual throttling pressure drop. Numerical simulation is necessary to optimize the nominal diameter;(5)Conventional completion can not adapt to development in heterogeneity reservoir, therefore ICD technology is more necessary. External casing packer (ECP) should be set in position of tremendous permeability change, in order to prevent annular flow disturbing ICD’s profile control.